In a large mixing bowl, combine the all-purpose flour, salt, and instant yeast.
Add the warm water to the dry ingredients and stir with a wooden spoon until a sticky dough forms.
Fold in the shredded sharp cheddar cheese, shredded mozzarella cheese, and garlic powder until evenly distributed.
Cover the bowl with plastic wrap or a clean kitchen towel and let the dough rise at room temperature for 12 to 18 hours, until the surface is dotted with bubbles and the dough has doubled in size.
Preheat the oven to 450°F (230°C). Place a Dutch oven or heavy oven-safe pot with a lid inside the oven to heat for 30 minutes.
While the oven and pot heat, lightly flour a clean surface and turn the dough out onto it. With floured hands, shape the dough into a ball by folding the edges toward the center. Let rest for 15 minutes.
After resting, shape the dough into a tight ball again and sprinkle the cornmeal onto a sheet of parchment paper. Place the dough ball on the parchment paper and drizzle the olive oil over the top.
Carefully remove the hot Dutch oven from the oven. Using the parchment paper, lift the dough and place it into the Dutch oven. Cover with the lid.
Bake covered for 30 minutes. Then remove the lid and bake for an additional 10 minutes until the crust is golden brown and crisp.
Remove the bread from the oven and transfer it to a wire rack. Let cool for at least 30 minutes before slicing.